In the travelling wire-type electrical machining, a continuous wire electrode is moved while being axially guided between support members under a suitable tension and a workpiece is disposed in juxtaposition with the wire electrode moving between the support members. Electric energy is applied between the moving wire electrode and the workpiece to remove material from the latter. The electric energy may be applied in the form of a series of electrical discharges when the machining fluid is constituted by a liquid dielectric or a continuous or pulsed electrolyzing current when the machining fluid is a liquid electrolyte. Sometimes, it is desirable to additionally provide abrasive machining action whereby electrical-discharge and/or electrolytic machining actions on the workpiece are facilitated. As material removal from the workpiece proceeds, the latter is displaced relative to the axially travelling wire-electrode in a prescribed path under numerical or mechanical copying control to achieve a desired cutting pattern.
When a plurality of cuts of an identical or similar pattern are to be made simultaneously in a workpiece or workpieces, it is convenient to arrange a single, continuous axially travelling wire electrode so that the latter is "multi-guided" between the support members in the form of the plurality of moving wire segments extending in parallel with one another. In the prior art, however, in which one output terminal of a machining power supply is connected to the workpiece and the other output is electrically connected to a single current conducting guide through which the single wire electrode travels, this measure has most often been unsuccessful or has yielded unsatisfactory results because of very frequent occurrence of the rupture of the wire electrode. This problem has now been found to be attributable to the fact that the wire electrode typically used is as thin in diameter as 0.05 to 0.5 mm so that the resistance varies from one wire segment to another, causing irregular current distribution between different wire segments and the workpiece. Further, once short-circuiting occurs at a certain wire location, the current flow will be concentrated at the short-circuited point, eventually causing wire breakage.